The present invention relates to multi-piece fastener more particularly to a high strength blind bolt using a lockbolt like swaged construction and providing a high final clamp load of workpieces secured together and further relates to such blind fasteners particularly adapted for constructions utilizing box beams or columns, bridges and the like.
The fastener of the present invention relates generally to multi-piece blind bolt fasteners which include a main sleeve, an expandable sleeve and a pin wherein the expandable sleeve is moved axially relative to the main sleeve and is expanded radially thereover to form a blind head in response to a relative axial force applied via the pin. In this regard the blind bolt of the present invention bears a general resemblance to a threaded blind fastener of the type shown in U.S. Pat. No. 3,643,544 issued Feb. 22, 1972 to Joseph H. Massa; fasteners of this type have been sold under the trade name Visu-Lok and/or Jo-Bolt by the Monogram Aerospace Fastener Company and Voi-Shan Manufacturing Company of the United States. See also U.S. Pat. No. 3,262,353 issued Jul. 26, 1966 to R. Waeltz et al, U.S. Pat. No. 2,765,699 issued Oct. 9, 1956 to J. LaTorre, U.S. Pat. No. 2,887,003 issued May 19, 1959 to Brilmeyer and U.S. Pat. No. 3,107,572 issued Oct. 22, 1963 to Orloff. The prior blind bolt fasteners, however, have certain problems since the main sleeve absorbs a significant portion of the clamp load developed and the clamp load, tensile strength and blind side protrusion can vary with grip range. In the present invention, however, a unique blind bolt construction is provided having a wide grip range capability and in which a high strength blind head of a uniform structure is formed over this wide grip range. Thus the blind head of uniform structure will have the same blind side protrusion over the grip range.
In one form of the invention, the high strength blind fastener includes a pin, an expandable or primary sleeve, a main or secondary sleeve, and a collar adapted to be swaged into lock grooves in the pin in response to a preselected relative axial force applied between the pin and collar. In the present invention the collar initially transmits an axial force from the swage anvil of the setting tool to the main sleeve. The pin has an enlarged head which transmits an opposite axial force against the expandable sleeve by virtue of a pulling force exerted by the tool. As the axial force increases, the expandable sleeve is moved axially relative to a tapered nose portion at the blind side of the main sleeve and is radially expanded to overengage that end of the main sleeve. In prior constructions, the amount of radial expansion of the blind head was determined by the angle of the tapered nose and its distance from the blind side of the workpieces being joined. Thus the shape and hence strength of the blind head could vary depending upon the nose angle and spacing of the expandable sleeve from the blind side surface. The pin head, of course, would not engage the tapered nose portion. Unlike prior constructions, however, the pin head is adapted to engage the nose portion of the main sleeve at which time the blind head is fully defined; the expandable sleeve and tapered nose portion, however, are provided to be of limited lengths such that the blind head is substantially fully formed when the pin head engages the nose portion and before the blind head engages the blind side of the workpieces. At this stage of the installation the workpieces have not been subjected to any clamp loads between the collar and the blind head via the pin. In order to bring the blind head into engagement with the blind side surface, the main sleeve is provided with a frangible portion which will fracture at a preselected magnitude of relative axial force whereby the tapered nose portion and the fully formed blind head can freely move axially; the fully formed blind head will then be brought into contact with the blind side surface of the workpieces with no axial restraint from the now severed, freely collapsible main sleeve. Now the workpieces are pulled together by the further application and increase in the relative axial pulling force substantially solely between the blind head and the collar via the action on the pin. The force clamping the workpieces together continues to increase until the collar is swaged into the lock grooves on the pin. The final clamp load on the workpieces can be determined first by an initial magnitude of relative axial force attained just before the collar starts to be swaged onto the pin and thereafter by elongation of the collar in response to swage. The initial axial clamp force on the workpieces is sometimes referred to as "pre-load" while the final clamping force after full swage is referred to as "final clamp load". The beginning of swaging at this pre-load is sometimes referred to as "primary clinch".
As noted with the fastener of the present invention, a unique construction is provided in which the "final clamp load" is maximized; at the same time the fastener can be provided with a wide grip range and the maximized "final clamp load" will be generally uniformly available over this wide grip range. One of the limitations with prior blind fasteners formed as noted is that a part of the relative axial force applied between the pin and collar is expended on the main sleeve. This is avoided in the present invention since the main sleeve is formed such that after the expandable sleeve has been expanded to form the blind head the main sleeve collapses or is axially deformed such that the relative axial force thereafter is applied substantially solely between the blind head and the collar via the pin. Thus, high clamp loads can be attained similar to that attainable by two piece lockbolt constructions such as that shown in U.S. Pat. No. 4,921,384 for Swage Fasteners With A High Stand-Off Collar by Keith Nordyke and issued May 1, 1990. As will be seen the collar design of the ' 384 patent can also, be advantageously utilized with the present invention.
In another form of the invention, a controlled tension type threaded nut and bolt construction is used. As will be seen, in this embodiment a nut member is threadably engaged on a threaded portion of the shank of the pin. A splined portion is located at the terminal end of the pin shank. An installation tool has a central socket member adapted to engage the splined portion and an outer wrench member adapted to grip the nut whereby torque can be applied between the two to provide relative rotation by which the nut is threaded onto the pin to attain the desired clamp up.
Thus the high strength blind bolt of the present invention is readily adapted for use in applications in which high strength bolts, such as SAE Grade 5 (ASTM A325) or higher, are frequently used. It is also desirable for use where blind welding, nut plates and other complex construction fastening systems are used. In this regard, the blind fastener of the present invention, because of its high clamp load, is especially suited for construction of buildings, bridges, and the like where high strength and durability are of considerable importance along with the capability of providing high clamp loads of the assembled parts. Thus the blind bolt of the present invention has a high tensile strength such as SAE Grade 5 or greater and/or the tensile strength of the Japanese Grade F8T bolt or greater. In addition the unique blind bolt construction, particularly in the pull-type swage version, will have the capability of providing a final clamp load of between around 70% to around 80% of the minimum ultimate tensile load of the fastener. This is accomplished, in part, by the use of high strength ferrous materials having a high hardness.
In another form of the invention the main sleeve is of a generally straight tubular construction, i.e. without a tapered nose portion, and the blind head is formed by bulbing, through column loading, the end of the expandable sleeve which is located beyond the blind side of the workpieces. In this regard, this latter form of the invention is generally of the type shown in U.S. Pat. Nos. 2,061,628 and 2,026,629 issued Nov. 24, 1936 to Huck, U.S. Pat. No. 2,114,493 issued Apr. 19, 1938 to Huck and U.S. Pat. No. 2,527,307 issued Oct. 24, 1950 to Huck. As with the prior embodiments, however, the blind head is first formed away from the blind side surface and the main sleeve will fracture or collapse at a higher relative axial force bringing the blind head into engagement with the blind side surface with no axial restraint from the collapsed main sleeve. Formation of the blind head at a preselected location can be facilitated by band annealing the expandable sleeve at a selected location. See in this regard U.S. Pat. No. 3,253,495 issued to Orloff on May 31, 1966. As will be seen the bulbed blind head can provide an enlarged bearing surface and hence be especially useful in applications in which the workpiece openings are substantially larger than the effective diameter of the fastener.